1. Field of the Invention
This invention relates to a motor formed in a rectangular or square shape.
2. Related Background Art
FIG. 1A of the accompanying drawings shows the construction of the essential portions of a motor disclosed in Japanese Laid-Open Utility Model Application No. 61-44637 and Japanese Laid-Open Utility Model Application No. 60-140934. A rotor 1 has a cylindrical rotor portion 1a with four poles on the circumference thereof, and a pinion 1b for outputting the rotation of said rotor 1 to a subsequent ring train, The rotor 1 is unitarily formed of a mixed synthetic resin material having magnetic powder mixed therewith. The poles of said rotor portion 1a and the teeth of said pinion 1b form a phase angle .theta.. A rotor shaft 2 is integrally secured to the central portion of the rotor. One end of said rotor shaft 2 is rotatably supported by a hole in a lower plate 3, and the other end of said rotor shaft 2 is rotatably supported by a hole in an upper plate 4 (not illustrated in FIG. 1A--see FIG. 2A). Each of stators 5 has a pair of legs so as to form a U-shape, and each end of the legs has a magnetic pole portion 5a opposed to the pole on the circumference of said rotor portion la, and the stators are so disposed that the ends thereof which are of the same shape are opposed to each other on the same plane, and are supported by the lower plate 3 and the upper plate 4. Two coils L1 and L2 for causing each magnetic pole portion 5a of said stator to produce a magnetic field, are connected to a driving circuit, not shown, and are inserted in the legs of said stator 5. The rotor 1, the rotor shaft 2, the lower plate 3, the upper plate 4, the stator 5 and the coils L1 and L2 together constitute a conventional PM type step motor M.
FIG. 2A of the accompanying drawings shows another motor of conventional construction disclosed in Japanese Laid-Open Utility Model Application No. 60-141682.
Referring to FIG. 2A, a rotor 1 comprising a permanent magnet magnetized with four poles in the diametrical direction thereof is integrally secured to a rotor shaft 2. One end of the rotor shaft 2 is rotatably supported by a hole in a lower plate 3, and the other end of the rotor shaft 2 is rotatably supported by a hole in an upper plate 4. Said one end of the rotor shaft 2 extends through the hole in the lower plate 3 and has secured thereto a coupling 5 for transmitting the rotation of the rotor 1 to a gear train. A stator 6 has a pair of legs so as to form a U-shape, and each end portion of those legs has a magnetic pole portion 6a opposed to the outer periphery of the rotor 1. Each magnetic pole portion 6a is formed so that the angle o thereof with respect to the center of the rotor is in a 90.degree. phase relation. There are provided two such stators 6 on the same plane and moreover, the magnetic pole portions 6a of one of the stators are disposed close to each other, and the phase relation between the magnetic pole portions 6a disposed close to each other is such that the angle .beta. thereof with respect to the center of the rotor 1 is 45.degree., and the stators are positioned by guide pins 3a provided on the lower plate 3. Further, two coils 7a and 7b for causing the magnetic pole portions 6a of the stators to produce a magnetic field are connected to a driving circuit (not shown), and said coils 7a and 7b are wound on coil frames 8, respectively, and are inserted in the legs of the stators 6 on that side thereof which does not have the magnetic pole portions 6a disposed close to each other. On the other hand, the lower plate 3 nd the upper plate 4 are formed by plastic molding, and the lower plate 3 has a restraining pawl 3b for mounting and fixing the upper plate 4, and the upper plate 4 has guide slots 4a into which the guide pins 3a of the lower plate fit, and a hooking portion 4b engageable with the restraining pawl 3b. After the two stators 6 into which the coils 7a and 7b have been inserted and the rotor 1 are mounted on the lower plate 3, the upper plate 4 is placed on the lower plate from above and the restraining pawl 3b and the hooking portion 4b are brought into engagement with each other, whereby the lower plate 3, the upper plate 4 and the stators 6 are fixed and the rotor 1 is rotatably supported.
FIGS. 1B and 2B of the accompanying drawings schematically show the arrangement relation between the rotors and the stators of the motors shown in FIGS. 1A and 2A, respectively.
Problems peculiar to the prior art will be mentioned below.
In the motors shown in FIGS. 1A and 2A, as shown in FIGS. 1B and 2B, the motor height T.sub.1 is great relative to the rotor diameter d, and the yoke width H.sub.2 is small relative to the rotor length L and thus, the magnetic flux cannot be designed to be great.
The cross-sections of the yokes are not identical in width to each other, such as H.sub.1 and H.sub.2, and this leads to a great number of working steps and a high cost.
The cross-sections of the yokes are not identical in width to each other, such as H.sub.1 and H.sub.2, and a clearance magnetic flux density of uniform intensity is not provided for the rotor length L, and if an attempt is made to make the magnetic flux density uniform, it is necessary that H.sub.2 =L, and H.sub.1 must be made greater.